Various methods for production and recovery of hydrogen and/or hydrogen-rich gas streams from gas mixtures obtained in steam reforming of natural gas and other methane-rich gas streams (SMR) are well known in the art. Processes have also been disclosed in which the reformate obtained from hydrocarbon steam reforming is subjected to a secondary oxidative operation in the presence of added air. In instances where the hydrogen product is intended for use in production of ammonia the amount of air employed in the secondary reforming step may provide all or part of the required nitrogen needed to satisfy the H.sub.2 /N.sub.2 stoichiometric ratio for NH.sub.3. Since oxides of carbon (CO and CO.sub.2) are present in the reformate as undesired contaminants, the reformate is subjected to a water gas shift reaction to convert contained CO to CO.sub.2 and then to procedures for removal of the CO.sub.2 and for conversion of any residual carbon oxides to methane (methanation). Such conventional methods for production of ammonia synthesis gas are described in Kirk-Othmer: Encyclopedia of Chemical Technology, third edition (1978), volume 2, page 488, FIG. 13.
The gas composition obtained by primary steam reforming of methane followed by secondary reforming in air, after undergoing a conventional shift reaction is comprised predominantly of hydrogen with lesser amounts of CO.sub.2 and nitrogen, constituting &gt; 98% of the total gas mixture. A typical composition may comprise (dry basis) for example:
______________________________________ Hydrogen 61.0 Carbon dioxide 18.0 Nitrogen 20.0 Carbon monoxide 0.5 Methane 0.3 Argon 0.2 ______________________________________